1. Field of the Invention
The present invention relates to a copier, facsimile apparatus or similar image forming apparatus of the type forming an image by an electrophotographic process.
2. Description of the Prior Art
It is a common practice with an image forming apparatus of the type described to uniformly charge the surface of an image carrier with a charger, electrostatically form a latent image on the charged surface of the image carrier, develop the latent image with toner stored in a developing unit to thereby form a corresponding toner image, and transfer the toner image to a sheet or recording medium. While the charger charges the surface of the image carrier by applying a current fed from a high-tension power supply, the charge to be deposited on the above surface is apt to become unstable due to, e.g., the wear or similar deterioration of the image carrier ascribable to aging and due to filming of impurities.
In light of the above, Japanese patent laid-open publication No. 5-010639, for example, proposes a system configured to sense a current returning from an image carrier charged by a charger to the ground of a high-tension power supply and executes, based on the current thus sensed, feedback control to the output of the power supply.
Today, there is an increasing demand for easy, efficient assembly and maintenance of the electric wirings that form a current feed path from high-tension power supply to a charger, a developing unit, image transferring unit or similar image forming section and a current return path that allows a current to be returned from the image forming section to the ground of the power supply, while saving spaces to be allotted to such wirings. To this end, it has been proposed to make one of a pair of support plates supporting, e.g., the axially opposite ends of an image carrier or those of an image forming section openable and mount the above electric wirings on the openable support plate.
More specifically, one of a pair of support plates, supporting an image carrier, an image forming section and so forth at axially opposite ends, generally supports a drive system while the other support plate is located to appear when the cover of an apparatus body is opened. The support plate, appearing when the cover of the apparatus body is opened, is made openable and allows, when opened, a person to maintain the image forming section or remove a sheet jamming it with the image carrier and image forming section held on the support plate on which the drive system is mounted. It is therefore possible to promote easy, efficient assembly and maintenance and save space by arranging electric wirings on the openable support plate.
However, a problem with the openable support plate scheme stated above is that when the support plate is opened, the contact portion of the image carrier and that of a member mounted on the support plate to form a current return path are apt to become unstable due to repeated opening and closing of the support plate. Consequently, the system configured to sense a current returning from an image carrier, as disclosed in laid-open publication No. 5-080639 mentioned earlier, is apt to fail to stably sense the current. Moreover, impurities deposited on the above contact portions or deterioration of the contact portions make current sensing more unstable, so that even the feedback control fails to stabilize the charge and maintain high image quality.